A typical motor grader has two front traction wheels (a left and a right) which can lean relative to neutral to one side or the other such that each front wheel assumes a present wheel-lean angle from neutral. Wheel-lean is provided in order to counter-act side-draft (i.e., lateral forces) caused by a moldboard angle of the moldboard of the motor grader. Extra weight on the front end can also be used to help counter-act side-draft.
Moldboard angle may be used in a variety of applications, ditching (i.e., cutting a ditch) and road maintenance (e.g., snow removal) being but two examples. Ditching typically involves large lateral forces, more so than typical road maintenance involving less material, and thus calls for more wheel lean than road maintenance. For example, it is known for an operator to perform a first job at a first job site (e.g., ditching) using wheel lean at a first wheel-lean angle, transition to a second job site with zero wheel lean (e.g., traveling over the road), and perform a second job at a second job site (e.g., road maintenance) with wheel lean at a second wheel-lean angle different from the first wheel-lean angle. Wheel lean is sometimes changed when turning between passes to sharpen the turn. Wheel lean is also used to make small steering corrections.
Neutral may assume a variety of orientations. It is known for neutral to be a normal to the surface on which the front wheels are positioned (e.g., the ground), the normal being vertical in the case of a flat, horizontal surface. It is also known for the front wheels to be designed with a positive camber at neutral (e.g., 0.21 degree) in order, for example, to lower the steering effort. In some graders, the camber of neutral is fixed. In other graders, the camber of neutral is adjustable.
The front wheels of a typical motor grader are leanable from neutral in order to change a present wheel-lean angle of the front wheels. With respect to each front wheel, a zero present wheel-lean angle means that the center-line of the wheel running through the top and bottom of the wheel is at neutral such that the present-wheel lean angle of the wheel relative to neutral is zero degrees. A non-zero present wheel-lean angle means that the wheel center-line is leaning or angled laterally to the left or right from neutral.
It is known for the front wheels to be connected to one another for coordinated wheel-lean of the front wheels. In some motor graders, a front axle is coupled pivotally to the main frame of the front section of the motor grader. At each end of the front axle is a yoke coupled pivotally to the axle. The left and right yokes are coupled pivotally respectively to left and right spindles using respective upper and lower kingpins. The left and right spindles are fastened respectively to left and right final drives, which are, in turn fastened respectively to the left and right front wheels. A hydraulic wheel-lean cylinder is coupled pivotally to the front axle and to, for example, the left yoke. The front wheels are connected to one another via a wheel-lean bar coupled to the yokes such that extension or retraction of the wheel-lean cylinder causes the present wheel-lean angles of the front wheels to change. The front wheels are thus coupled to opposite ends of a front axle to move relative thereto to lean at a present wheel-lean angle from neutral.
A human operator can control wheel lean from the operator's station with an input device (e.g., a control lever), by relying on visual references. For example, a type of visual indicator has a mark on the front axle and a mark on the wheel-lean bar. Relative alignment or misalignment of the marks provides a visual indication of wheel lean.
In another example, operators have estimated wheel lean from observation of one or both of the wheels. Operator feedback of premature tire wear resulted in a past solution that reduced the amount of positive camber in the front wheels at neutral, to address situations where an operator may be returning one of the wheels to vertical while the other wheel is leaning (considering that a system with front wheel camber of a degrees at neutral would result in a wheel lean of 2α at one wheel if the other wheel is returned to vertical).
When the operator attempts to return the wheels to neutral by use of such visual references, the wheels sometimes end up leaning away from neutral due to inherent accuracy limitations of these methods. If the wheels are leaned away from neutral, pre-mature tire wear can result when roading a motor grader at high speeds on, for example, concrete or asphalt surfaces or other wear-inducing surfaces.